Anaesthesia and Analgesia of fish Dr Stewart Fielder Port Stephens - - PowerPoint PPT Presentation

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Anaesthesia and Analgesia of fish

Dr Stewart Fielder Port Stephens Fisheries Institute

Marine fish production and enhancement

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Plan of talk

• Who uses anaesthetics for fish
• Why anaesthetics are used
• When anaesthetics are used
• How anaesthetics are used
• What types of drugs are used
• Preparation and monitoring needed
• Euthanasia
• Analgesia

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Who uses anaesthetics on fish

• Aquaculture (range of procedures)
• Fish research (e.g. zebra fish,

600 labs globally)

• Public zoos and aquaria wanting

to provide improved veterinary care of their fish

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Do fish feel pain?

Contentious! Both sides of the argument set the same requirements for pain reception but opinions differ on where the criteria appear phylogenetically and whether or not parallel systems have evolved in different classes and species. Nevertheless, Fish display robust neuroendocrine and physiologic stress responses to noxious stimuli

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Why is chemical restraint needed

• Increase safety for fish and handler
• Procedures can be done out of water
• Reduces movement and physiologic changes in

response to pain stimuli

• Reduces excitement and hyperactivity related

trauma that can occur in routine handling = lowers mortality and morbidity

• Decreased movement minimises integuement

damage and osmoregulatory disturbances,

• Reduces metabolism and oxygen demand and

produces less waste (CO2 and ammonia)

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When is anaesthesia used

• fish handling
• post-harvest transportation
• diagnostic procedures
• surgery/gavage
• artificial breeding

broodfish anaesthetised to enable gamete sampling, hormone injection, and egg and milt stripping

• euthanasia.

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How are anaesthetics administered

• Immersion = inhalation

drug ventilated in solution enters bloodstream via gills/skin passes rapidly to CNS

Most common method

• Parenteral
• ral (metomidate only one?)

intravaenous injection Intracoelomic injection Intramuscular injection (hand syringe, pole syringe, darting)

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Drugs used for IMMERSION anaesthesia

• Tricaine methane sulphonate (MS-222)
• Benzocaine
• Clove Oil, Eugenol, Isoeugenol, Aqui-S
• Metomidate
• 2-Phenoxyethanol
• Quinaldine & Quinaldine sulphate
• Azaperone
• Medetomidine (atipamezole 6x dose for recovery)
• Isoflurane and Halthane
• Oxygen (for some sharks)

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Drugs used for PARENTERAL anaesthesia

• Ketamine (IM, IV)
• Medetomidine + ketamine (IM; atipamezole for

recovery in some sharks)

• Xylazine + ketamine (IM)
• Propofol (IV)
• Alfaxolone/Alfadolone (for sensory physiology)

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Why select a particular anaesthetic

• Efficacy (rate of induction/recovery, margin of safety, adverse

responses)

• Ease of use – administration (mixing, water solubility, pH )

disposal

• Toxicity to users
• Cost

Most widely used immersion anaesthetic (isoeugenol)

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Aqui-S advantages

• Approved in Australia, NZ, Norway, Korea, Costa Rica,

Honduras with Zero withholding period

• Soluble in freshwater and seawater
• Effective at low concentration 5-20mg/L
• Sedative effects detected at low concentrations
• Wide margin of safety – fish can remain in treatment for long

periods of time

• Limited adverse response
• Fast recovery
• Cost effective

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Levels of anaesthesia in fish

From Barker et al., 2009

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Essential preanaesthetic preparation

• 1. Baseline behavioural parameters (ventilation, caudal fin

stroke rate, overall activity level, schooling behaviour)

• 2. No food for 12-24 h – limits regurgitation (clogs gills /

nitrogenous waste)

• 3. Containers with adequate water for transportation,

induction, maintenance, recovery, possible water changes

• 4. Water quality same as source water (DO, pH, temp,

salinity)

• 5. Out of water plan to prevent drying (skin, fins, eyes)
• 6. PPE (masks for powders, gloves)

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Monitoring

Anaesthetic depth (e.g. activity, reaction to stimuli, equilibrium, jaw

tone, muscle tone, caudal fin strokes, swimming, respiratory rate)

• Usually occurs within 5-10 minutes
• ften a short excitement phase during immersion; coughing reflex

Cardiopulmonary Activity (can be monitored with cardiac

ultrasonography, Doppler flow probes, ECG; blood gas sampling for O2, CO2 and pH)

Water Quality (DO, pH, temp, ammonia) Recovery (occurs when fish returned to aerated, anaesthetic-free

water; often 5-10min; might show excitement phase – protect fish and handler)

Resuscitation (may require forward movement through water or

irrigation of gills)

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Sedation (5 ppm Aqui-S)

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Light anaesthesia (10 ppm Aqui-S)

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Gavaging medicated feed Heavy (surgical) anaesthesia (20 ppm Aqui-S)

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Euthanasia

Overdose of immobilization drug is usually acceptable

• Mostly use Immersion drugs MS-222 and benzocaine

at 5 -10x anaesthetic concentration

• Large fish - poured onto gills
• Maintaining fish in solution 5-10 mins after cessation
• f opercular movement = expired
• Cardiac asystole lags behind brain death (myocardial

cells use local glycogen stores)

• Or cranial concussion, pithing, spinal transection,

exsanguination used in deeply anaesthetised fish

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Analgesia

Limited information is available about the use of analgesics in fish

• Drugs listed as anaesthetics are often assumed to

provide analgaesia if they result in complete immobilisation of the fish but depends on drug property – caution needed!

• Some studies with morphine (rainbow trout) and

butorphanol (koi carp) have shown some analgaesic or at least antinociceptive action

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ACEC Guideline NSW Fisheries

http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0010/114976/ACEC-Guide-2009- FINAL-VERSION.pdf